The present invention relates generally to systems for controlling actuation of a variable position valve, and more specifically to systems for maintaining accurate control over opening and closing events of an EGR valve for an internal combustion engine.
When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). One known technique for reducing unwanted emissions such as NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx.
In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold.
EGR operation is typically not required under all engine operating conditions, and known EGR systems accordingly include a valve, commonly referred to as an EGR valve, for controllably introducing exhaust gas to the intake manifold. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.
EGR valves must typically be robust enough to maintain a commanded position despite disturbances caused by pressure variations across the valve, yet at the same time be sensitive enough to provide for quick valve opening and valve closing response times. Because valve closing events are typically required to occur very quickly, many overly aggressive EGR valve control arrangements suffer from the drawback that damage to the valve may occur during seating. What is therefore needed is an EGR valve control system directed to overcoming this and other drawbacks associated with prior art EGR valve control systems.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a method of controlling operation of an EGR valve comprises the steps of monitoring an EGR valve command provided to control position of an EGR valve, stepwise forcing the EGR valve toward a closed position if said EGR valve command corresponds to a valve close command, monitoring EGR valve position, and ramping the EGR valve to said closed position when said EGR valve position is within a threshold distance from said closed position.
One object of the present invention is to provide an improved EGR valve control system operable to close the valve in a rapid stepwise fashion to a position short of a valve closed position, and to then more slowly ramp the valve to the closed position to thereby prevent damage to the valve and/or valve seat.
Another object of the present invention is to provide an EGR valve control system configured to schedule higher control gains during valve closing events than during valve non-closing events.
A further object of the present invention is to provide a PID controller-based EGR valve control system incorporating an integrator anti-windup feature operable to stop integration when integration limits are exceeded or when further integration worsens the extent of saturation.
Yet a further object of the present invention is to provide an EGR valve control system incorporating a battery compensation feature operable to maintain the DC gain of the system constant regardless of battery voltage level.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.